1. Field of the Invention
The present invention relates to self-aligning connector apparatus. More particularly, the present invention pertains to threaded couplings, such as are utilized between pipe members and the like, and to techniques for aligning two members to be threadedly connected to avoid cross-threading, for example. The present invention finds particular application in the general area of drilling and working wells such as oil and gas wells, wherein tubing such as casing members of relatively large diameter are frequently connected together into strings by mutual threaded engagement.
2. Description of Prior Art
Threaded connections between pipe members are typically made by providing one end of one pipe member with a male connector in the form of an externally threaded pin member, and providing an end of the second pipe member with a female coupler in the form of an internally threaded box member which receives the pin member. The pin and box members may be integral parts of their respective pipe members, or may be added thereto by welding or threaded engagement, for example. In particular, various collars and nipples are known featuring combinations of two box ends, two pin ends, or a box end with a pin end for threaded connection to appropriate ends of two pipe members sought to be mutually connected. Additionally, various thread constructions are known, including tapered threads and straight threads, for example. The different threaded designs are intended to serve particular purposes in some instances. For example, an effective metal-to-metal fluid seal may be provided by joining complementarily tapered threads in a pin and box connection. Further, a variety of threads are known for use in various thread structures.
In the area of well casing, a standard design of eight round threads per inch or five buttress threads per inch may be used. The lengths of the threads in such cases range from about approximately two inches on relatively small outside diameter (OD) casing, such as five inch casing, to five inches on larger OD casing, such as twenty inch casing. Generally, as the OD of casing increases by a factor of four, the length of the threads on such casing only increases by a factor of two and a half. Additionally, the number of threads per inch for a given type of thread is generally the same for casing of all OD's. As a result, it may be expected to be more difficult to stab larger OD casing, and the likelihood of cross-threading the pin and box threads of such larger casing also increases.
It is desirable and advantageous to acquire a technique to assist in the alignment of pipe members for mutual theaded connection sufficiently to ensure that cross-threading between the pipe members cannot occur.